As a core technology of a next generation transport network, an optical transport network (Optical Transport Network, OTN) includes electrical-layer and optical-layer technical specifications, and provides comprehensive operation, administration and maintenance (Operation, Administration and Maintenance, OAM), a powerful tandem connection monitoring (Tandem Connection Monitoring, TCM) capability, and an out-of-band forward error correction (Forward Error Correction, FEC) capability. The OTN technology can implement flexible dispatching and management of large-capacity services, and is gradually becoming a mainstream technology of a backbone transport network.
At an electrical processing layer, the OTN technology defines a standard encapsulation structure, maps various customer services, and can implement management and monitoring of the services. A structure of an OTN frame is shown in FIG. 1. The OTN frame is a structure of 4×4080 bytes, that is, 4 rows×4080 columns. The structure of the OTN frame includes a framing area, an OTUk (Optical Channel Transport Unit, optical channel transport unit) OH (Overhead, overhead), an ODUk (Optical Channel Data Unit, optical channel data unit) OH, an OPUk (Optical Channel Payload Unit, optical channel payload unit) OH, an OPUk payload area (Payload Area), and a FEC area, where values 1, 2, 3, and 4 of k correspond to rate levels 2.5G, 10G, 40G, and 100G respectively. The framing area includes a FAS (Frame Alignment Signal, frame alignment signal) and an MFAS (Multi-frame Alignment Signal, multi-frame alignment signal). Information in the OPUk OH is primarily used for mapping and adaptation management of a customer service, information in the ODUk OH is primarily used to manage and monitor an OTN frame, and information in the OTUk OH is primarily used to monitor a transmission section. A fixed rate of an OTUk is referred to as a line interface rate. Currently, line interface rates at four fixed rate levels 2.5G, 10G, 40G, and 100G are available. The OTN transmits a service in the following manner: an upper-layer service is mapped to an OPUj at a lower rate level, and an OPUj overhead and an ODUj overhead are added to form an ODUj, which may be referred to as a lower-order ODUj; then the lower-order ODUj is mapped to an OPUk at a higher rate level, and an OPUk overhead, an ODUk overhead, an OTUk overhead and a FEC are added to form a fixed-rate OTUk, which is referred to as a higher-order OTUk; the higher-order OTUk is modulated onto a single optical carrier for transmission, where a bearer bandwidth of the optical carrier is equal to the fixed rate of the higher-order OTUk. In addition, an ODUflex is introduced into the conventional OTN, and is referred to as a lower-order variable-rate optical channel data unit. The ODUflex is used to carry an upper-layer service at any rate. First, the lower-order ODUflex needs to be mapped to a higher-order OPUk, and an OPUk overhead, an ODUk overhead, an OTUk overhead and a FEC are added to form a fixed-rate higher-order OTUk, and then the higher-order OTUk is modulated onto a single optical carrier for transmission.
Explosively growing, flexible, and varied upper-layer customer IP (Internet Protocol, Internet Protocol) services have resulted in a pressing need for an optical transport technology beyond 100G, such as a 400G or 1T rate. This has posed a significant challenge for a conventional optical transport network system, and long-distance and high-rate transmission also needs to be supported. However, existing optical spectrum resources are divided according to a 50 GHz optical spectrum grid slot width, and a 50 GHz optical spectrum grid slot width is allocated to each optical carrier. For optical carriers whose bearer bandwidths are at four fixed rate levels 2.5G, 10G, 40G, and 100G, an optical spectrum width occupied by the optical carriers does not reach 50 GHz, leading to a waste of optical spectrum resources. Optical spectrums are limited resources. To fully use optical spectrum resources, improve overall transmission capabilities of a network, and implement transmission of ever-increasing upper-layer customer IP (Internet Protocol, Internet Protocol) services, a Flex Grid (flexible grid) technology is introduced into an optical layer. The Flex Grid technology is a variable spectral width technology, and extends optical spectrum resources from fixed 50 GHz optical spectrum grid slot division (ITU-T (International Telecommunication Union-Telecommunication Standardization Sector-Telecommunication, International Telecommunication Union-Telecommunication Standardization Sector-Telecommunication) G.694) to optical spectrum grid slot division at a smaller granularity. Currently, a minimum optical spectrum grid slot width is 12.5 GHz, and therefore one signal may occupy multiple consecutive optical spectrum grids.
Because the signal occupies multiple consecutive optical spectrum grids, available spectrums of an optical fiber may have a large number of idle spectrum areas, that is, spectrum fragments. As shown in FIG. 2, spectrum fragments 1 and 2 are generated in carrier groups 1, 2, and 3. When a new service needs to be transmitted, if spectral widths of the spectrum fragments 1 and 2 are less than a spectral width required by the new service, there are no available consecutive spectrum resources. Therefore, usage of the spectrum resources is low.
A network planning algorithm is adopted in the prior art to properly allocate spectrum resources of an optical fiber in advance for a specific network structure and service transmission requirements. Although this algorithm can optimize spectrum resource allocation to some extent, this algorithm cannot fundamentally avoid congestion because services are dynamically transmitted. A multi-carrier transport technology is adopted at an optical processing layer, and multi-carrier transmission based on a variable quantity of carriers is implemented by using a comb light source or multiple independent light sources, a multiplexer, a demultiplexer, and multiple modulators in the optical domain. However, a service interruption problem occurs in a subcarrier frequency change process. Therefore, hitless migration of spectrums between multiple carrier groups cannot be implemented.